Cutting nozzle assembly for a postmixed oxy- fuel gas torch

ABSTRACT

A novel cutting nozzle assembly for a postmixed oxygen-fuel gas torch is disclosed. The nozzle assembly includes a cylindrical shroud which surrounds and extends away from the gas discharge orifices in the gas discharge end of the cutting nozzle. The cylindrical shroud has the advantage of producing a tighter gas stream and of promoting a more thorough mixing of the preheat oxygen and the fuel gas to provide a hotter, more compact flame which produces a more parallel-sided cut through metal workpieces. The cutting tip therefore conserves metal as well as cutting gases. It also cuts faster than prior art postmixed cutting nozzles.

This is a divisional of application Ser. No. 07/981,352, filed Nov. 25,1992, now U.S. Pat. No. 5,700,421.

FIELD OF THE INVENTION

The present invention relates to oxy-fuel gas torches and, inparticular, to a cutting nozzle for postmixed oxy-fuel gas torches.

BACKGROUND OF THE INVENTION

Oxy-fuel gas cutting torches are useful for cutting ferrous alloys. Withthe proper equipment, cuts can be effected through very thick billets.In operation, an oxy-fuel torch is used to direct an ignited stream ofoxygen and fuel gas onto the surface of the metal to be cut. The metalis thus heated to its ignition temperature, at which point a stream ofcutting oxygen directed at the surface oxidizes the heated metal toeffect the cut.

The cutting torch may be one of a premixed or a postmixed type torch. Ina premixed torch, preheat oxygen and fuel gas are mixed within the torchhead before being discharged for ignition. In a postmixed cutting torch,the preheat oxygen and fuel gas are discharged from the torch in unmixedstreams. Turbulence in the discharged streams mixes the oxygen and fuelgas before ignition occurs. A principal advantage of the postmixedcutting torch is that it is not subject to flashback, a potential hazardassociated with the use of premixed torches. Flashback occurs when theoxygen and fuel gas mixture in a premixed torch ignites within the torchhead. Postmixed torches are therefore preferred for heavy industrialapplications where a torch is subjected to considerable heat. A furtheradvantage of the postmixed torch is that postmixed nozzles produce alonger heat zone than premixed nozzles. This permits the postmixed torchto operate farther from the work, decreasing the heat stress on thetorch and the increasing service life of the nozzle.

An example of a prior art postmixed oxy-fuel gas cutting torch andnozzle are taught in the U.S. Pat. No. 4,455,176 which issued to Fuhrhopon Jan. 19, 1984. That patent describes a combination cutting torch andnozzle assembly for post-mixed oxy-fuel cutting using two separateannular streams of preheat oxygen gas surrounding the fuel gas streamwith the inner annular preheat oxygen stream directed to impinge thefuel gas stream very close to the point of discharge from the nozzleassembly. The nozzle assembly is secured to the head of the cuttingtorch by a hollow retaining nut which forms an annular gap with thenozzle assembly for discharging the outer preheat oxygen gas stream.

All prior art postmixed nozzles for oxy-fuel gas torches operate insubstantially the same way. A stream of cutting oxygen is dischargedfrom an axial bore in the nozzle. A plurality of fuel gas dischargeorifices arranged in a concentric ring around the axial bore dischargepreheat fuel gas and a second plurality of gas discharge orificesarranged in an outer concentric ring discharge preheat oxygen which actsas an envelope that surrounds the fuel gas stream. As the gas streamsflow toward the workpiece, a mixing of the fuel gas and the oxygenoccurs and the mixture ignites to heat the workpiece.

Testing has shown that up to 50% of the preheat oxygen stream dischargedfrom prior art postmixed torch nozzles is lost to the atmosphere beforemixing with the fuel gas occurs. This contributes to inefficientcombustion and slows the heating process. It also contributes to thecost of cutting since gases are not utilized to their potential. It hasalso been observed that prior art postmixed torch nozzles are incapableof effecting a parallel-sided cut through a thick workpiece. The cut isnarrower along a top of the workpiece than along a bottom of theworkpiece. The thicker the workpiece, the wider the cut at the bottomside. If many thick billets must be cut, a significant loss of metaloccurs.

A further disadvantage of prior art cutting nozzles for postmixedoxy-fuel gas torches is their direct exposure to splashback of moltenmetal from the cut. Splashback metal tends to stick to the discharge endof the nozzle, frequently blocking discharge orifices. When this occurs,the torch must be shut down to permit the nozzle to be cleaned orreplaced. This interrupts workflow and increases operating expenses.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a cutting nozzle assemblywhich overcomes the disadvantages of the prior art.

It is a further object of the invention to provide a cutting nozzleassembly which promotes more efficient combustion of oxy-fuel gasmixtures.

It is yet a further object of the invention to provide a cutting nozzleassembly which minimizes nozzle damage due to the splashback of moltenmetal onto the discharge end of the nozzle.

It is yet a further object of the invention to provide a cutting nozzleassembly which provides a cleaner cut that minimizes the loss of metalduring a cutting operation.

In accordance with the invention there is provided a cutting nozzle fora postmixed oxy-fuel gas torch, comprising a nozzle assembly having anaxial bore through which cutting oxygen gas is discharged and a firstand second plurality of spaced-apart gas discharge bores arranged in aninner and an outer concentric ring around the axial bore, the inner ringbeing in fluid communication with a fuel gas conduit of the torch whenthe cutting nozzle is coupled to the torch and the outer ring being influid communication with a preheat oxygen gas conduit of the torch whenthe cutting nozzle is coupled to the torch, the axial bore and the gasdischarge bores terminating in discharge orifices on a discharge end ofthe cutting nozzle; and a shroud surrounding and extending away from thedischarge end of the cutting nozzle to protect the nozzle from cuttingsplashback and to promote a mixing action of the gases discharged fromthe nozzle.

The present invention therefore provides a cutting nozzle assembly for apostmixed oxy-fuel gas torch having a shroud which extends away from thedischarge end of the nozzle to protect the discharge end of the nozzlefrom molten metal splashback and to concentrate, direct, and promote themixing of the oxygen/fuel gas streams. This results in a narrower,cleaner more parallel-sided cut which conserves metal at the cut andincreases the speed and efficiency of cutting. The service life of thenozzle is further increased because the discharge end of the nozzle isshielded from splashback. Molten metal splashback having a trajectorywhich enters the throat of the shroud is generally cooled by the gasstream to a point that it does not fuse with the nozzle before itcontacts the nozzle discharge end. Nozzles in accordance with theinvention have been operated for weeks under industrial work conditionswithout requiring maintenance or replacement.

In accordance with a first embodiment of the invention, the shroud is anintegral part of the retainer nut used to couple the nozzle to the torchand the retainer nut further includes a flange which is pierced withbores that discharge the preheat oxygen. This embodiment is particularlycost efficient to produce because it minimizes the quantity of metalrequired in the nozzle as well as the machining time required to formthe nozzle assembly.

In accordance with a second embodiment of the invention, the shroud isan integral part of a retainer nut which is used to couple the nozzle tothe torch, but the nozzle includes all of the gas discharge bores.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will be more fully describedby way of example only and with reference to the following drawings,wherein:

FIG. 1 is a longitudinal cross-sectional view of a preferred embodimentof a postmixed torch nozzle assembly in accordance with the invention;

FIG. 2 is a top plan view of the postmixed nozzle assembly shown in FIG.1;

FIG. 3 is a longitudinal cross-sectional view of a second embodiment ofa postmixed nozzle assembly in accordance with the invention;

FIG. 4 is a top plan view of the postmixed nozzle assembly shown in FIG.3;

FIG. 5 is a partial cross-sectional view of the postmixed nozzleassembly shown in FIG. 1 coupled to a postmixed cutting torch; and

FIG. 6 is a schematic view of a cut through a 43/4 inch steel billeteffected with a prior art cutting nozzle and a cut through the samebillet effected with a cutting nozzle in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a longitudinal cross-sectional view of a cutting nozzle inaccordance with a preferred embodiment of the invention. The cuttingnozzle assembly, generally referred to by reference 10, includes anozzle 12 and a hollow retainer nut 14. The nozzle 12 includes an axialbore 16 for discharging cutting oxygen from a cutting torch (see FIG.5), a plurality of fuel gas bores 18 arranged in an inner concentricring around the axial bore 16, and a plurality of preheat oxygen bores20 arranged in an outer concentric ring around the axial bore 16. Eachof the bores 16, 18 and 20 terminates in a discharge orifice 22, 24 and26 respectively in a discharge end 28 of the cutting nozzle assembly 10.

The retainer nut 14 surrounds the nozzle 12 and is used to couple itwith a cutting torch (see FIG. 5). In accordance with the preferredembodiment of the invention, an annular flange 15 in an inner peripheryof the retainer nut 14 forms a portion of the discharge end 28 of thecutting nozzle assembly 10. The retainer nut 14 includes a spiral thread30, a hexagonal rib 32 to provide a gripping surface for a wrench, and ashroud 34 which surrounds and extends away from the discharge end 28 ofthe cutting nozzle assembly 10. The shroud 34 is preferably a circularcylinder although other cylindrical shapes may also be used.

As described above, the retainer nut 14 preferably forms a part of thedischarge end 28 of the cutting nozzle assembly 10. The hollow retainernut 14 surrounds the nozzle 12. The preheat oxygen bores 20 in thenozzle 12 communicate with a cavity 36 in the retainer nut 14. Theannular flange 15 of the retainer nut 14 is provided with preheat oxygenbores 38 which communicate with the preheat oxygen discharge orifices26. Thus, preheat oxygen entering preheat oxygen bores 20 passes throughthe cavity 36 in the retainer nut 14 and exits through the preheatoxygen bores 38 via the preheat oxygen discharge orifices 26. Thisconfiguration of the cutting nozzle assembly 10 provides the mosteconomically produced assembly because it minimizes drilling andmaterial requirements.

FIG. 2 shows a top plan view of the cutting nozzle assembly 10 shown inFIG. 1. As is apparent, the hexagonal rib 32 of the retainer nut 14provides a gripping surface for a wrench to facilitate coupling thecutting nozzle assembly to a torch. The shroud 34 surrounds thedischarge end 28 of the cutting nozzle. The discharge end 28 includesdischarge orifices 22 for cutting oxygen, 24 for fuel gas and 26 forpreheat oxygen. The discharge orifice 22 for cutting oxygen ispreferably flared. This creates a swirl effect within the interior ofthe shroud 34 to promote the mixing of fuel gas and oxygen. The shroud34 also shields the discharge end 28 from molten metal splashed backfrom the cut. This enhances the service life of the nozzle because itsubstantially eliminates nozzle damage resulting from splashback metalcontacting the nozzle and fusing with it.

FIG. 3 is a longitudinal cross-section through a second embodiment ofthe invention. The cutting nozzle assembly is substantially identical instructure to the assembly shown in FIGS. 1 and 2. In this embodiment,the nozzle 12 includes all of the discharge bores. The retaining nut 14supports the shroud 34. The cutting oxygen discharge orifice 22, thefuel gas discharge orifices 24 and the preheat oxygen discharge orifices26 are all located in the discharge end 28 of the nozzle 12. In allother respects, the cutting nozzle assembly 10 as shown in FIG. 2 isidentical to the cutting nozzle assembly 10 shown in FIG. 1. Thisembodiment of the invention requires slightly more material tomanufacture as well as more machining time but produces identicalcutting results.

FIG. 4 shows a top plan view of the nozzle shown in FIG. 3. The nozzleis identical to the embodiment shown in FIG. 2 except that there is noseam between the fuel gas discharge orifices 24 and the preheat oxygenorifices 26.

Cutting nozzle assemblies 10 are preferably constructed from brassalloy, although other materials such as copper, stainless steel and thelike may also be used. The shroud 34 is preferably at least 0.65" (16.5mm) long. Longer lengths may be used but much shorter lengths are notrecommended. The thickness of the sidewall of the shroud 34 ispreferably about 0.22" (5.58 mm) for good resistance to heat fatiguealthough a thinner sidewall may be used successfully. At least the outersurface of the sidewall of the shroud 34 is preferably plated withchrome or nickel to inhibit the adhesion of molten metal splashback.

FIG. 5 shows the cutting nozzle assembly 10 illustrated in FIG. 1connected to a typical postmixed oxy-fuel gas torch. The oxy-fuel gastorch includes a torch head 40 to which the cutting nozzle fuel assemblyis coupled using the retainer nut 14. The torch head 40 is supported bya tubular handle 42. The tubular handle is hollow. Extending through thetubular handle are supply tubes for cutting oxygen, fuel gas and preheatoxygen. Supply tube 44 supplies cutting oxygen from an oxygen source.Supply tube 46 supplies fuel gas from a fuel gas source, and supply tube48 supplies preheat oxygen from the oxygen source. The fuel gas supplytube 46 and the cutting oxygen supply tube 48 terminate in radialdistribution grooves 50 and 52, respectively. The operation of postmixedoxy-fuel gas torches is well understood by those skilled in the art.

FIG. 6 shows a schematic diagram of two steel billets cut using apostmixed oxy-fuel gas torch. Each billet is approximately 43/4" (12 cm)thick. A first billet 54 was cut using a typical prior art postmixedcutting nozzle. A second billet 56 was cut using a cutting nozzle inaccordance with the invention. As is apparent, the kerf of the cutthrough the second billet 56 is narrower and more parallel-sided thanthe kerf of the cut through the first billet 54. The kerf of the cutthrough the first billet 54 is approximately 0.305" (7.75 mm) wide wherethe cut commences at the top surface 58 of the first billet. The kerf isapproximately 0.478" (12.14 mm) wide at the bottom surface 60 of thefirst billet 54. In contrast, the width of the kerf at the top surface62 of the second billet 58 is approximately 0.21" (5.33 mm) wide and thekerf at the bottom surface 64 of the second billet 56 is alsoapproximately 0.21" (5.33 mm) wide. It is, therefore, apparent that thecutting nozzle in accordance with the invention cuts a much thinner kerfand produces cut ends which are much more square than kerfs achievedwith the prior art postmixed nozzles tested. Experimentation has beenestablished that a postmixed cutting nozzle in accordance with theinvention produces 40% less slag than a prior art nozzle of the sametype. In a production environment, this represents a considerable savingin energy and cut materials. The cleaner kerf produced by a cuttingnozzle assembly 10 in accordance with the invention is due to thetighter, more cylindrical gas discharge stream promoted by the shroud 34(see FIGS. 1 through 5). The shroud 34 promotes a more thorough mixingof the preheat oxygen and the fuel gas and produces a gas stream thatmaintains its shape over a much longer distance than a gas streamdischarged by prior art postmixed nozzles.

Industrial Applicability

The cutting nozzle for a postmixed oxy-fuel gas torch in accordance withthe invention is useful in cutting steel and other ferrous alloys,particularly in industrial production environments such as steel millswhere large slabs must be cut into billets for handling or processing.Because the cutting nozzle provides a cleaner and narrower cut thanprior art nozzles of the same type, the nozzle conserves materials andenergy. The cutting nozzle assembly also has a prolonged service lifebecause it is less susceptible to damage due to the splashback of moltenmetal. Operating overheads are therefore reduced. The cutting nozzleassembly 10 in accordance with the invention may be used in anyapplication where metals must be rapidly and efficiently cut byoxidation.

It is therefore apparent that a new and useful cutting nozzle forpostmixed oxy-fuel gas torches has been invented.

The embodiments described above are intended to be exemplary only. Thoseskilled in the art will understand that certain prior art postmixednozzle constructions may be modified to accord with the invention bywelding or soldering a shroud to either the retainer nut or thedischarge end of the prior art nozzle or by redesigning a retainer nutto include an integral shroud. Changes and modifications to thespecifically described embodiments may be made without departing fromthe scope of the invention which is intended to be limited solely by thescope of the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method of cuttingmetal using a postmixed oxy-fuel gas torch having a nozzle including adischarge end connected by gas passages to an intake end adapted to bein fluid communication with the postmixed oxy-fuel gas torch, and ashroud which surrounds and extends in an axial direction away from thedischarge end of the nozzle to an open end, comprising the steps ofconducting cutting oxygen gas, preheat oxygen gas and fuel gas from thetorch through the gas passages to the discharge end of the nozzle forinitial mixing within said shroud, shaping the flow of gases with theshroud so that the resulting flame effects a more narrow and parallelwalled cut of metal to conserve metal at the cut and increase theefficiency of cutting.
 2. The method of claim 1, wherein the step ofshaping the flow of gases with the shroud includes forming a flow ofcutting oxygen surrounded by a flow of fuel gas.
 3. The method of claim2, wherein the step of shaping the flow of gases with the shroud furtherincludes forming a flow of preheat oxygen surrounding said flow of fuelgas.
 4. A method of promoting a downstream mixing of the gasesdischarged from a postmixed oxy-fuel gas torch nozzle comprising thestep of: discharging the gases through a postmixed nozzle having ashroud that surrounds and extends away from a discharge end of thenozzle.
 5. A method of maintaining a tighter cylindrical shape along agreater flow distance of cases discharged from a postmixed cuttingnozzle of a postmixed oxy-fuel gas torch, comprising the step of:discharging the gases through a postmixed nozzle having a shroud thatsurrounds and extends away from a discharge end of the nozzle.
 6. Themethod of claim 1, further including a step of extending the shroud asufficient distance beyond the discharge end of the nozzle to causesplashback metal entering the shroud to cool sufficiently to inhibitfusing of the splashback metal to the discharge end of the nozzle,thereby protecting the discharge end of the nozzle during metal cutting.7. A method of cutting metal using a postmixed oxy-fuel gas torchcomprising the steps of: attaching a nozzle to the torch, the nozzleincluding a discharge end connected by gas passages to an intake endadapted to be in fluid communication with the postmixed oxy-fuel gastorch, and a shroud which surrounds and extends in an axial directionaway from the discharge end of the nozzle to an open end; conductingcutting oxygen gas, preheat oxygen gas and fuel gas from the torchthrough the gas passages to the discharge end of the nozzle; andoperating the postmixed oxy-fuel torch to cut the metal.
 8. The methodof claim 7, further including a step of shaping the flow of gases withinthe shroud means by forming a flow of cutting oxygen surrounded by aflow of fuel gas.
 9. The method of claim 8, wherein the step of shapingthe flow of gases within the shroud by forming a flow of preheat oxygensurrounding said flow of fuel gas.
 10. The method of claim 7, furthercomprising a step of extending the shroud from the discharge end of thenozzle to protect the nozzle from molten metal splashback during metalcutting by extending the shroud a sufficient distance beyond thedischarge end of the nozzle to cause splashback metal entering theshroud to cool sufficiently to inhibit fusing to the discharge end ofthe nozzle.
 11. A method of cutting metal with a postmixed oxy-fuel gastorch having a nozzle and for protecting the nozzle against metalsplashback occurring during metal cutting, said nozzle including adischarge end connected by gas passages to an intake end adapted to bein fluid communication with the postmixed oxy-fuel gas torch, and ashroud which surrounds and extends in an axial direction away from thedischarge end of the nozzle to an open end, comprising the steps ofconducting cutting oxygen gas, preheat oxygen gas and fuel gas from thetorch through the gas passages to the discharge end of the nozzle forinitial mixing within said shroud, and protecting the discharge end ofthe nozzle with the shroud from molten metal splashback during metalcutting.
 12. A method of effecting a more narrow and parallel walled cutof metal to conserve metal at the cut and increase the efficiency ofcutting using a postmixed cutting tip mounted to a postmixed oxy-fuelgas torch nozzle comprising the step of: discharging the gases through apostmixed nozzle having a shroud that surrounds and extends away from adischarge end of the nozzle.
 13. The method of claim 11, wherein thestep of initial mixing within the shroud includes forming a flow ofcutting oxygen surrounded by a flow of fuel gas.
 14. The method of claim13, wherein the step of initial mixing within the shroud includesforming a flow of preheat oxygen surrounding said fuel gas flow.
 15. Themethod of claim 11, wherein the step of protecting the discharge end ofthe nozzle with the shroud from molten metal splashback during metalcutting includes extending the shroud a sufficient distance beyond thedischarge end of the nozzle to cause splashback metal entering theshroud to cool sufficiently to inhibit fusing of the splashback metal tothe discharge end of the nozzle.